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The danger of drug-resistant parasitic hookworms in dogs

By Zarwareen Khan, May 17 2023—

Pet dogs are prevalent across many parts of the world, such as the U.S., which has the largest population. The Gauntlet interviewed Abinaya Venkatesan, a Ph.D. candidate with Dr. John Gilead at the Faculty of Veterinary Medicine, who has studied drug-resistance parasites infecting both dogs as well as humans. 

There are multiple species of parasites, specifically parasitic nematodes, that can infect a wide range of hosts. Therefore, there are various species of worms, such as hookworms (Ancylostoma caninum), that infect dogs as well. These parasites have been prevalent in dogs for thousands of years through migration and they are a part of our ecosystem as well. 

“This particular hookworm, it’s one of the most prevalent parasites of dogs in the USA. However, in Canada, you can find hookworms in the southern parts of the country where temperatures are slightly warmer. But there are also other species of hookworms that are very prevalent in Canada as well,” said Venkatesan. 

Hookworms can be transferred from the mother to the puppy through lactation. As puppies are prone to worm infections because they have not yet acquired immunity to deal with them, breeders often give them a deworming dosage or even three. Parasitic nematodes, such as helminths, are treated with drugs called anthelmintics, and with frequent deworming, anthelmintic resistance has been widespread in both puppies and livestock animals.

“We’ve seen that with bacteria, we’ve seen that even with COVID, the virus, for example,” said Venkatesan. “Where the initial vaccines that were designed against specific strains of COVID, the coronavirus are not effective against the later evolved strains of the coronavirus. So all of these parasites, bacteria, virus, they all undergo very rapid mutations, which gives them an evolutionary advantage to kind of resist the action of drugs.” 

Seven years prior, another Ph.D. student in the lab was invested in using a specific type of molecular detection method, known as deep amplicon sequencing. This method uses next-generation sequencing techniques, which are seen widely in biological research as well. Essentially, the genes that cause drug resistance in parasites are identified, sequenced and then a part of them are sequenced in order to look for the specific mutation that will give rise to the resistance. 

“So it’s more like a screening protocol really, where you’re like looking for, you’re sequencing a section of the gene of the parasite and then you’re looking for specific mutations or amino acid substitutions in these parasites,” she said. “So that’s the method that we used to detect widespread resistance.”

Initially, this study was a spin-off of another project conducted in 2021, where drug resistance in racing greyhounds was studied. Greyhound racing is a big industry in the U.S. but has rapidly declined in the last few decades due to animal welfare concerns. Essentially, greyhounds are kept in enclosed spaces, which favours the transmission of parasites. As such, they are often subjected to anthelmintic treatment in order to be healthy. Ultimately, it was found that there was high resistance of hookworms in the racing greyhound population, which raised questions about the state of this condition in pet dog populations in the U.S.

“So now we know that in the U.S., there’s widespread resistance, but there’s a very high chance that there’s also widespread resistance in so many other countries,” explained Venkatesan. “It’s only gonna be a matter of time before these parasites develop resistance to every drug class there is and we all know that developing new drugs is a very lengthy and tedious process.”

It takes decades of research to bring a new drug to the market, and if parasites are resistant to the ones that are currently available, there will be no way to treat certain diseases or infections. Therefore, it is necessary to proceed with caution when using these drugs.

“​​We are investigating more into what the spreads and origin of parasite transmission are,” said Venkatesan. 

For example, parasites are spread through feces, and that is why it is important that dog owners are able to pick up after their dogs. This is especially true when considering dog parks, where many dogs interact with one another. If their feces are left on the ground, the chance of another dog contacting these feces is high, and thus so is the spread of parasites. Furthermore, if a dog is not responding positively to one type of drug class, a combination should be used in order to delay the spread of resistance.

“One of our biggest concerns with the results of this research is, unfortunately, the same drugs that are being used to treat parasitic infections in animals are also being used in humans,” said Venkatesan. “Because they’re the same kind of parasites as well.”

In developing countries, parasitic worm infections are still prevalent. The WHO has taken measures to control these infections, such as through the mass drug administration (MDA) program. Using drug donations from bigger companies, this program is responsible for distributing tablets, such as anti-parasitic tablets, to children in schools in endemic regions.

“But what they don’t realize is, given the situation that we’ve seen in animals, that such a frequent administration of these drugs leads to drug resistance, there’s a high probability that it’s also going to happen with parasites of humans,” she said.

When an individual who carries resistant parasites travels to other countries, they will likely spread said resistant parasites as well. However, there are still a lot of parasites that are refugia, which refers to a certain population of parasites that have not been exposed to drugs. 

“Most of these parasites are found in the soil and everything, but then when a person consumes a pill, it’s only gonna affect the parasites inside the person’s system,” explained Venkatesan. “The rest of the parasites in the environment are still not bothered by these drugs. So that helps maintain the susceptible population of parasites.”

Although refugia are prevalent in humans at the moment, it is still important to consider the harmful effects of drug resistance and its implications on human health. If drug resistance does emerge, even if it is seen in a small population, it is only a matter of time before it will spread across the world. 

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